1. Field of the Invention
The present invention relates to a video transmission system using plural links and, more particularly, to a video transmission system using plural links suitable for transmitting compressed video signals.
2. Description of the Related Art
Multiple video transmission through different links has been conventionally used for enhancing reliability of transmission. One example of such conventional transmission will be described below in reference to FIG. 6.
FIG. 6 illustrates a duplex video transmission using regular and backup links. An input video signal 40 is distributed to two links by a distributor 41. In the case of digital compression coding transmission, encoders 42 and 44 for video signal compression and decoders 43 and 45 are used in the two links, respectively. Assuming that the link consisting of the encoder 42 and the decoder 43 is referred to as a regular link and the link consisting of the encoder 44 and the decoder 45 is referred to as a backup link, a switcher 46 selects the regular link at the time of normal transmission, to output an output video signal 47. To the contrary, in the case where an accident occurs on the regular link, the switcher 46 immediately switches the transmission link to the backup link, to thus output an output video signal 47.
In this way, the above-described duplex video transmission using the regular and backup links can ensure the high reliability of the video signal transmission.
However, the above-described duplex video transmission using the regular and backup links has raised a problem that the transmission links are used with low efficiency since the backup link is not used at all during the normal transmission which accounts for most of the transmission period of time.
An object of the present invention is to provide a video transmission system using plural links in which the transmission capacity of a backup link can be effectively used while high reliability of transmission can be ensured.
The first aspect of the invention lies in that a video transmission system using plural links for transmitting video signals over the plural links comprises means for distributing an input video signal to the plural links, and processing means for coding the video signals distributed to the links in such a manner as to shift them from each other at least either spacewise or timewise.
The second aspect of the invention lies in that a video transmission system using plural links for transmitting video signals over the plural links comprises decoding means for decoding the coded video signals transmitted over the plural links, synthesizing means for synthesizing the video signals from the plural links decoded by said decoding means, the video signals being shifted from each other at least either spacewise or timewise, and output selecting means for selectively outputting the decoded outputs on the links and an output from said synthesizing means, said output selecting means selecting the output from said synthesizing means when the plural links are operated normally while selecting the decoded output on the normal link in the case where abnormality occurs on any one of the plural links.
The third aspect of the invention lies in that a video transmission system using plural links for transmitting video signals over the plural links comprises means for distributing an input video signal to the plural links, processing means for coding the video signals distributed to the links in such a manner as to shift them from each other at least either spacewise or timewise, decoding means for decoding the coded video signals transmitted over the plural links, synthesizing means for synthesizing the video signals from the plural links decoded by said decoding means, the video signals being shifted from each other at least either spacewise or timewise, and output selecting means for selectively outputting the decoded outputs on the links and an output from said synthesizing means, said output selecting means selecting the output from said synthesizing means when the plural links are operated normally while selecting the decoded output on the normal link in the case where abnormality occurs on any one of the plural links.
According to the present invention, the video signals on the links are coded in such a manner as to be shifted from each other at least either spacewise or timewise, so that the video signals transmitted over the plural links are synthesized, thereby obtaining the output video signal similar to the original video signal. Furthermore, it is possible to obtain a normal video signal also over a single link.